The invention relates to a liquid curable resin composition exhibiting excellent light resistance and suitable as a coating material for optical fibers, optical fiber ribbons, and the like, and to a cured product thereof.
In the manufacturing of optical fibers, resin coatings are provided over glass fibers prepared by spinning a molten glass for protection and reinforcement. As such a resin coating, a structure consisting of a primary flexible coating layer formed on the surface of optical fibers and a secondary rigid coating layer applied thereon is known. Optical fiber ribbons comprising a number of fibers provided with the above resin coatings bundled side by side on the same plane by using bundling materials are also well known. Resin compositions for primary coating layers, secondary coating layers, and bundling materials for optical fiber ribbons are designated as primary materials, secondary materials, and tape materials, respectively. These resin coatings are usually provided by curing a liquid curable resin composition applied on the surface of the optical fibers by using heat or light, in particular, ultraviolet rays.
Since optical fibers are used over a long period of time, the coating material used for the optical fibers must exhibit only a slight change in properties over a long period of time.